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Long-duration insurance contracts - Summary of changes in discounted present values of expected future policy benefits and expected future net premiums (Detail) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward] |  |
Balance at September 30 | $ 18,275 | $ 18,612
Periodic Payment Annuity [Member] |  |
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward] |  |
Balance at beginning of year | 10,276 | 11,212
Balance at beginning of year at original discount rate | 11,757 | 11,681
Effects of actual versus expected experience | (17) | 2
Change in benefits, net | (373) | (357)
Interest accrual | 417 | 411
Foreign currency effect | 110 | 96
Ending balance at original discount rate | 11,894 | 11,833
Effects of changes in discount rate assumptions | (1,316) | (697)
Expected future policy benefits at September 30 | 10,578 | 11,136
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward] |  |
Balance at September 30 | 10,578 | 11,136
Liabilities for future policy benefits at September 30, net of reinsurance recoverables | 10,578 | 11,136
Life and Health [Member] |  |
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward] |  |
Balance at beginning of year | 43,784 | 52,665
Balance at beginning of year at original discount rate | 55,170 | 65,871
Effects of cash flow assumption changes | (138) | 1,485
Effects of actual versus expected experience | 199 | (12,709)
Change in benefits, net | (1,434) | (1,404)
Interest accrual | 981 | 891
Foreign currency effect | 1,728 | 218
Ending balance at original discount rate | 56,506 | 54,352
Effects of changes in discount rate assumptions | (11,122) | (11,111)
Expected future policy benefits at September 30 | 45,384 | 43,241
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward] |  |
Balance at beginning of year | 39,294 | 46,916
Balance at beginning of year at original discount rate | 49,500 | 58,731
Effects of cash flow assumption changes | (97) | 1,449
Effect of actual versus expected experience | 164 | (11,033)
Change in premiums, net | (1,418) | (1,348)
Interest accrual | 879 | 791
Foreign currency effect | 1,604 | 200
Ending balance at original discount rate | 50,632 | 48,790
Effect of changes in discount rate assumptions | (9,969) | (10,005)
Expected future net premiums at June 30 | 40,663 | 38,785
Balance at September 30 | 4,721 | 4,456
Reinsurance recoverables | (52) | (52)
Liabilities for future policy benefits at September 30, net of reinsurance recoverables | $ 4,669 | $ 4,404

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